Olefins are used to produce many useful products. For example, ethylene and/or propylene are polymerized to produce polymer, such as polyethylene, polypropylene, ethylene-propylene copolymer, etc. Olefins are produced by many conventional processes, including: (1) catalytically converting alcohol, such as methanol; (2) pyrolysing a hydrocarbon-containing feed, as in steam cracking; or (3) catalytically cracking a hydrocarbon feed, as in fluidized catalytic cracking, hydrocracking, etc. Besides olefins, effluents from these processes contain acidic gases for example, H2S and/or CO2. The effluent also contains diolefin molecules for example, propadiene, cyclopentadiene, isoprene, or butadiene. Additionally, the effluent can contain aldehyde, such as acetaldehyde.
Amine may be utilized for removing one or more acidic gases from a process stream containing olefins. For example, CO2 and H2S are removed from a steam cracker effluent by contacting the effluent with an amine mixture by an acid gas scrubbing process in an absorber.
Inside the absorber, the amine mixture absorbs acid gases, like CO2 and H2S, and removes them from the olefins process stream. The amine mixture containing the acid gases exits the absorber and is conducted to an amine regeneration system where the mixture is heated in a regenerator to release the acid gases and produce a regenerated amine mixture. Conventional designs of amine regenerators cool the regenerator overhead to produce a reflux liquid that is sent back to the regenerator tower. The regenerated amine mixture exiting the regeneration system, mostly free of acid gases, is returned to the absorber where the process is repeated.
A significant hurdle to operation of an acid gas scrubbing process is buildup of polymerized foulant, particularly in the regeneration equipment. Polymerization fouling causes the acid gas scrubbing process to limit capacity for the broader olefin production process resulting in significant negative financial impact.
One way to lessen polymerization fouling in the amine regeneration system involves contacting the amine with an aromatic stream such as pyrolysis gasoline to remove a majority of foulant precursors upstream of the regenerator. See, e.g., U.S. Pat. No. 3,926,591, incorporated by reference. Foulant precursors are transferred to the aromatic stream, producing a rich aromatic stream (i.e., an aromatic stream rich in foulant) which is conducted away from the process. However, even with this known procedure, it is not possible to keep all the foulant precursors away from the regeneration system. As a consequence, polymerization fouling of regeneration system equipment, particularly equipment in and downstream of the regenerator that is contacted by the foulant-containing regenerated amine, remains a capacity limiting problem for the broader olefin process.
U.S. Pat. No. 6,989,046, incorporated by reference, describes adding a heavy hydrocarbon solvent upstream of the regenerator and leaving a portion of the solvent entrained in the amine being fed to the regenerator. However, the specific gravity of the heavy hydrocarbon solvent limits separation and removal efficiency. Further, adding solvent upstream of the regenerator leads to undesirable solvent in the regenerator overhead stream.
Pending U.S. patent application Ser. No. 14/629,602, incorporated by reference, describes adding aromatic hydrocarbon downstream of the regenerator.
Nevertheless, fouling in amine systems, particularly in or downstream of the regenerator, remains a limitation to operating run-length and capacity.